1. Field of the Invention
This invention relates to the formation of titanium silicide contacts for VLSI interconnections prior to the formation of insulating layers therearound.
2. Brief Description of the Prior Art
In the formation of very large scale integrated (VLSI) circuits, contact has been made to active layers of the semiconductor material disposed below the surface thereof by the process of etching of holes through insulating layers and the deposition of electrically conductive material into the etched holes or apertures. This procedure has operated very successfully in the prior art circuits wherein the horizontal dimensions of the etched apertures have exceeded the vertical dimensions of such apertures by a substantial amount. Under these prior art conditions, the conductor deposited into the apertures finds no problem passing to the bottom of the apertures and making contact with the active semiconductor or other layers at the bottom of the etched regions. However, with the continual shrinkage in the dimensions of the circuit elements of the integrated circuits, it has been necessary that the apertures utilized for making contact to active and other regions below the surface of the semiconductor device be continually decreased in dimension. While this decrease in dimension has in fact been made for the horizontal dimension, the layer thicknesses have remained substantially the same, thereby requiring that the vertical dimension remain substantially as they have been in the past. The result of this situation is that, as the circuit elements continue to shrink in size, the horizontal dimensions of such apertures as described above gradually approach those of the vertical dimension and may even be exceeded by the vertical dimension. Under these circumstances, it has been found that it is extremely difficult to etch the apertures of required dimension and then proceed to apply conductive material into the aperture which can in fact continually make contact to the active or other region at the bottom of the aperture and extend up to the surface of the device. The result of this problem is apparent and is a falloff in the yield and end product reliability that can be obtained. In view of the above noted problems, it is apparent that new methods for making electrical contact to active or other layers below the surfaces of semiconductor devices must be changed to alleviate the presently existing problem.